In a communication system in which data is transferred by packets, a ranging method in which a receiver, in a given ranging window, periodically compares received data with expected data to find a match. The method includes establishing a communications link between the mobile device and the alternative device. The cutter is movable to a distal position to sever tissue protruding through the transverse aperture. If the right table hash value matches a hash table value, the actual values are compared.